1. Field of the Invention
The present invention relates to a sheet transport apparatus having a puncher for punching a hole in the sheet, and more particularly, to a sheet transport apparatus having the function of, for example, sorting, or a sheet transport apparatus for use in an image forming apparatus such as a copying machine.
2. Description of the Related Art
Previously, in order to file in a binder a sheet bundle output from an image forming apparatuses such as a printer and a copying machine, sheet hole punchers were provided separately from the apparatuses.
These hole punchers punched by one operation the ejected sheet bundle having images formed thereon, and it was necessary to set the sheet bundle manually in the hole puncher, thereby decreasing productivity. In addition, in cases where the bundle had a large number of sheets, punches and dies of the punchers were overloaded, and a significant force was required for punching. At the same time, the punches and the dies wore out, resulting in bad punching and the production of burrs. Therefore, it was necessary to perform several punching operations by dividing the sheet bundle into a predetermined number of sheets, and this further decreased productivity.
A sheet processing device has been proposed in which a hole puncher is provided on a transport path, and a sheet bundle loaded on a processing tray provided in the image forming apparatus is hole punched in one operation. This allows for the previous operation of setting the sheet bundle in the puncher to be omitted, thereby increasing operational efficiency.
In the above device, however, the next sheet cannot be transported during the punching operation of the sheet bundle while the sheet bundle loaded on the processing tray is being punched in one operation, and it is difficult to increase the sheet transporting speed of the image forming apparatus. In addition, the punching operation must be performed for each of a predetermined number of sheets due to the fact that the sheet bundle is punched in one operation.
Thus, a sheet processing device shown in FIG. 9 has been proposed in which a multiple-hole puncher 51 composed of a rotary punch 52 and die 53 is provided on a sheet transport path 50, and the sheet transport speed is in synchronization with the rotation speed of the punch 52 and die 53. With this, the sheets P in transportation can be punched one by one without stopping transportation of the sheet.
In the above conventional device, however, a burr P1 may sometimes be produced around a punched hole of a sheet P when the sheet P is cardboard, and the punch 52 and the die 53 are worn. At this time, since the sheet P passes through the sheet transport path 50 after the punching operation, the burr P1 rubs over the inner wall of the sheet transport path 50 to generate frictional resistance. This may generates flaws and tears on the sheet P, and cause bad transportation.
In addition, as shown in FIGS. 10A and 10B, in a sheet processing device, such as a sorter, in which the sheet P is ejected on an eject tray 54 and registered, the trailing end of the sheet P to be ejected may be caught by the burr P1 of the previously ejected and loaded sheet P to cause bad loading. In addition, when performing registration in the direction perpendicular to the direction of ejection, punched holes of the previously ejected sheet P and the later ejected sheet P may be caught by each other to cause bad registration.